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  • Insert cover image for Chapter 7 (p. 170).
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7 7 Presentation Transcript

  • Chapter 7: Air Masses and Weather Systems Physical Geography Ninth Edition Robert E. Gabler James. F. Petersen L. Michael Trapasso Dorothy Sack
  • Ch. 7: Air Masses and Weather Systems
  • 7.1 Air Masses
    • Air Mass: large body of air whose temperature and moisture characteristics are similar.
    • Due to General Atmospheric Circulation, air masses move and cause changing weather.
    • Source Region:
      • m = maritime (sea)
      • c = continental (land)
      • E = Equatorial (very warm)
      • T = Tropical (warm)
      • P = Polar (cold)
      • A = Arctic (very cold)
  • 7.1 Air Masses
  • 7.1 Air Masses Q: Which air mass affect your location? Are there seasonal variations?
  • 7.1 Air Masses
    • Air Mass Modification
      • cP or CA moves over Great Lakes and picks up moisture, and may cause Lake effect snow.
  • 7.1 Air Masses
    • Continental Arctic (cA): Dry and very cold
      • occasionally impacts U.S. in the winter
      • it often produces record breaking cold.
    • Continental Polar (cP): Dry and cold.
      • May reach Gulf of Mexico in winter.
      • Rarely affects west coast.
    • Maritime Polar (mP): moist and cool
      • Westerlies bring air mass to west coast, especially in winter. Occasionally affects east U.S.
  • 7.1 Air Masses
    • Maritime Tropical (mT): moist and warm
      • May originates in Gulf of Mexico
      • Major impact on central and eastern U.S
        • T-storms in the summer
        • Clashes with cP
    • Continental Tropical (cT): dry and hot
      • Small source region (SW deserts and N. Mexico
      • Dry line
      • Smallest player in U.S. weather
  • 7.2 Fronts
    • Fronts
      • clash between air masses
      • Generally move with westerlies
      • 3-dimensional
      • Frontal uplift
  • 7.2 Fronts
    • Cold Front:
      • Cold air moves in on warm air
      • Warm air (less dense) rises above cold air
      • Steep slope
      • Cumulonimbus
      • may form a Squall line
      • Sharp changes in temperature, pressure, and wind
  • 7.2 Fronts
    • Warm Front:
      • Warm air moves in on cooler air
      • Warm air (less dense) rises above cold air
      • Slope is not as steep
      • Light precipitation which may last longer
      • Usher in warmer conditions
  • 7.2 Fronts
    • Stationary Front
      • Boundary between air masses that is not moving
      • Extended period of light precipitation and occasionally strong T-storms
    • Occluded Front
      • Cold air is overtaking warm air
      • Dying storm
  • 7.2 Fronts
    • Four Major Frontal Symbols used on weather maps.
  • 7.3 Atmospheric Disturbances
    • Middle Latitude Cyclones
      • Common location for a clash between cold, polar air and warm, subtropical air
      • Convergence
      • Guided by polar jet stream
      • Variable weather
  • 7.3 Atmospheric Disturbances
    • Cyclones (L)
      • Move with jet stream/westerlies
      • Converging, rising air
      • Fronts
      • Precipitation
    • Anticyclone (H)
      • Move with path of westerlies
      • Divergence, sinking air
      • Dry weather
  • 7.3 Atmospheric Disturbances
    • Horizontal and Vertical Structure of pressure systems
    • Where would the strongest and weakest winds be?
  • 7.3 Atmospheric Disturbances
    • Common track of storms (mid-latitude cyclones)
    • What storm track (jet stream) influences your location?
  • 7.3 Atmospheric Disturbances
    • Stages in the development of a mid-latitude cyclone
    • Q: Where would you expect precipitation. Why?
  • 7.3 Atmospheric Disturbances
    • Cyclones and Local Weather
    • Q: Describe the front(s), temp, air mass type, wind direction, and precip. at Des Moines, St Louis, and Pittsburg.
  • 7.3 Atmospheric Disturbances
    • Cyclones and Upper Air Flow
    • Polar jet stream
    • Major impact on temperature and precip.
    • Q: Where would you expect storms to develop?
  • 7.3 Atmospheric Disturbances
    • Polar Jet Stream Analysis
    • Anticyclones
    • Q: Which country does most of this pattern occupy? Where is an anticyclone?
  • 7.3 Atmospheric Disturbances
    • Hurricanes
      • Circular, cyclonic storm with wind speeds greater than 74 mph (118 km/hr)
      • Smaller than mid-latitude cyclone
      • Same air mass type
      • More destructive
      • Also called tropical cyclones
  • 7.3 Atmospheric Disturbances
    • Cross section of a hurricane
  • 7.3 Atmospheric Disturbances
    • Storm Surge
    • Q: Why is the timing of landfall so critical to coastal areas?
  • 7.3 Atmospheric Disturbances
    • Major “Hurricane Alleys”
    • Which coastlines seem unaffected by these tracks?
  • 7.3 Atmospheric Disturbances
    • Hurricane development
      • Warm water (>25 o C or 77 o F)
      • Most air
      • Coriolis force (do not form or survive near equator)
    • Stages of Development
      • Tropical disturbance
      • Tropical depression
      • Tropical Storm (become named)
      • Hurricane (categorized by Saffir-Simpson Scale)
  • 7.3 Atmospheric Disturbances
    • Saffir-Simpson Scale
  • 7.3 Atmospheric Disturbances
    • Three hurricane tracks
    • Subtropical High (Bermuda High)
  • 7.3 Atmospheric Disturbances
    • Hurricane Strikes
    • Q: What areas of our coasts seem to have escaped landfall?
  • 7.3 Atmospheric Disturbances
    • Snow Storms and blizzards
      • Mid and high latitudes
    • Blizzard
      • Severe weather event
      • Heavy snow and strong winds (55 km/hr or 35 mph)
      • Visibility reduced
  • 7.3 Atmospheric Disturbances
    • Thunderstorms
      • Low and mid latitudes
      • Lightning: intense discharge of electricity
      • Thunder: sonic boom created by the expansion of air around the lightning bolt
      • Usually cover a small area
  • 7.3 Atmospheric Disturbances
    • Types of Thunderstorms
      • Convective (thermal)
      • Orographic
      • Frontal
  • 7.3 Atmospheric Disturbances
    • Tornadoes
      • Occur almost anywhere but are most common in North America (Tornado Alley)
      • Small intense, cyclonic storm of low pressure, violent winds, and converging air
  • 7.3 Atmospheric Disturbances
    • Destruction caused by an F5 tornado in Greensburg, Kansas on May 16, 2007
  • 7.3 Atmospheric Disturbances
    • Average annual # of tornadoes
    • and seasonal variation
  • 7.3 Atmospheric Disturbances
    • Doppler radar:
      • improves tornado detection and forecasting
      • Able to determine wind speed and direction
    • Q: How many squall lines can you see on this image?
  • 7.3 Atmospheric Disturbances
    • Fujita Scale (F-0 to F-5)
    • Enhanced Fujita Scale (EF-0 to EF-5)
  • 7.3 Atmospheric Disturbances
    • Weak tropical Disturbances
      • Easterly Wave
      • Polar Outbreak
  • 7.3 Atmospheric Disturbances
    • Weather Forecasting
      • Doppler radar
      • Weather satellites (e.g. GOES East)
      • High speed computers
      • Improving!
  • Physical Geography End of Chapter 7: Air Masses and Weather Systems